Raise the settings menu in the layering scale

poc/public/style.css

@@ -1578,10 +1578,15 @@ a.vk-attachment:hover {
 
 /* Settings overlay */
 
+/*
+ * Layering scale, highest wins:
+ *   chrome 40 · media view 70 · media modals 95 · settings 1000 · toasts 1100
+ * Any new full-screen layer should pick a slot below 1000, not above the dialogs.
+ */
 .vk-overlay {
     position: fixed;
     inset: 0;
-    z-index: 80;
+    z-index: 1000;
     display: flex;
     justify-content: flex-end;
     background: color-mix(in srgb, var(--color-neutral-900) 55%, transparent);
@@ -1905,7 +1910,7 @@ a.vk-attachment:hover {
     position: fixed;
     right: 16px;
     bottom: 16px;
-    z-index: 100;
+    z-index: 1100;
     display: flex;
     flex-direction: column;
     gap: 8px;